Support collect_env on Windows

[del-zhenwu]

As the following code shows, tail command can not be executed on Windows.

mmcv/mmcv/utils/env.py

Line 60 in 9fa5de8

f'"{nvcc}" -V | tail -n1', shell=True)

15:52:32  C:\Users\user\miniconda3\envs\mmcvv1.4.0_cuda111_py36_torch1.8.0\lib\site-packages\wheel\bdist_wheel.py:87: RuntimeWarning: Config variable 'WITH_PYMALLOC' is unset, Python ABI tag may be incorrect
15:52:32    sys.version_info < (3, 8))) \
15:52:38  1.8.0
15:52:38  1.4.0
15:53:06  'tail' 不是内部或外部命令，也不是可运行的程序
15:53:06  或批处理文件。
15:53:06  'gcc' 不是内部或外部命令，也不是可运行的程序
15:53:06  或批处理文件。

[zhouzaida]

closed by #1789